Two-piece sheet metal bell-crank lever construction



Nov. '18, 1969 A. PROVI ETAL 3,478,618

TWO-PIECE SHEET METAL BELL-CRANK LEVER CONSTRUCTION 2 Sheets-Sheet 1 Original Filed April 28, 196'? FIG. 2

S l R VR 0 OT T W m Pu G W A I m E B O R S Nov. '18, 1969 A. PROV! ETAL TWO-PIECE SHEET METAL BELL-CRANK LEVER CONSTRUCTION Original Filed April 28, 1 967 2 Sheets-Sheet E FIG. 4

FIG. 5

INVENTORS MIKE A. PROV! 8. ROBERT GUINTER United States Patent Int. Cl. Gg 4/04 US. Cl. 74-519 '8 Claims ABSTRACT OF THE DISCLOSURE The two-piece bell-crank lever is made of two sheet metal stampings, one a generally triangular shaped bracket and the other a T-shaped body member disposed in right angle relationship, the bracket having a downwardly facing hook projection at its upper and engaging in a notch in the top of the body at the middle thereof, while a lug projecting from the inner end of the bracket in downwardly spaced relation to the hook enters a registering hole provided in the body, the inner edge of the bracket being generally V-shaped to match a generally V-shaped bend in the body, so that when the two pieces are placed between dies with the hook engaging loosely in the notch and the lug started entering the hole, and the dies are closed to crimp the body transversely between the hole and notch, the two pieces are pressed together entering the lug in the hole and tightly engaging the hook in the notch, the two pieces are rigidly and permanently connected by swaging the hook into the notch and upsetting the projecting end ofthe lug at the hole.

This application is a division of our co-pending application, Ser. No. 641,096, filed Apr. 28, 1967.

This invention relates to a two-piece sheet metal bell crank lever construction, which, while especially designed for use in bathroom scales when made of the appropriate small size, especially for bathroom scales of greatly diminished height-nearly half the height of what was previously considered a low scale, is not necessarily limited to such use, being, of course, adapted to be constructed in various sizes for various other uses.

In the bathroom scale application, of these levers, the scale measured only 1 and /s inches high as against previous scales measuring 1 and A; inches to 2 inches in height, the radical reduction in height being attainable by a substantially complete reorganization and rearrangement of the lever mechanism, so that whatever parts require any appreciable movement linearly are arranged to have this movement in a substantially horizontal plane between the closely spaced sheet metal base or bottom pan and the sheet metal platform. Thus, four of these small bell-crank levers are provided fulcrumed on the base on knife edges to support the platform on these levers at four widely rectilinearly spaced points, two of which are at opposite ends of each of two substantially parallel horizontally disposed bars reciprocable horizontally relative to the base and platform in closely spaced parallel relation to the base to transfer the weight measuring force exerted on the levers by the loaded platform to these bars with a relatively small amount of linear motion given said bars, this small motion being then multiplied by two long horizontally disposed levers that are fulcrumed relative to the base and connected with and extending from the bars inwardly toward one another to transmit increased movement horizontally to a member attached on the one hand to the readout rack and on the other hand to the weighting spring and disposed horizontally between the base and platform, the linear movement 3,478,618 Patented Nov. 18, 1969 given this member in the stretching of the weighing spring being indicated in any suitable way for a weight reading, as, for example, by the rotation of a dial relative to a pointer.

The reorganization and rearrangment of the lever mechanism also necessitated a completely new design and novel construction of bell-crank levers for weight transfer, each consisting of a generally T-shaped main body part in which the cross-bar portion of the T defines the two flat-bottomed trunnions mentioned above, while the vertical leg portion of the T, which has a cross-bar on its lower end for an easy pivotal tie-on connection with one end of one of the horizontal bars by insertion first through a longitudinally extending slot in the bar and then turning the leg at right angles, has a V-bearing formed thereon on one side closely above the cross-bar for fulcrum engagement therein of a transverse knife edge provided on the bar at one end of the slot. The T-shaped 'main body part supporting on the opposite side thereof from the V-bearing, in a plane at right angles thereto and on its vertical center line, a generally triangular vertical bracket which has a V-notch in the top edge thereof in which to seat the middle knife edge of a conventional generally U-shaped platform supporting hangar disposed transversely of the bracket in spaced substantially parallel relation to the T-shaped main body part of the bell-crank lever. The fastening together of the triangular bracket plate and the T-shaped lever in rigid right angle relationship to one another is accomplished in a novel manner, making these bell-crank lever assemblies available at lower cost but in a better form than would be possible with other constructions costing a lot more.

The invention is illustrated in the accompanying drawings in which:

FIG. 1 is a plan view of a low bathroom scale utilizing the improved bell-crank levers of our invention, this view being with the platform removed and most of the dial broken away so as better to reveal the structure therebeneath;

FIG. 2 is a longitudinal section on the line 2-2 of 1 FIG. 1 showing'the parts as they appear when the platform is under load and the weighing spring is stretched;

FIG. 3 is a partial section similar to FIG. 2 but illustrating the relationship of the parts when the platform is not under load, as in FIG. 1;

FIG. 4 is a sectional detail on the line 4--4 of FIGS. 1 and 5 showing the parts enlarged;

FIG. 5 is a cross-section on line 55 of FIG. 4 and FIG. 6 is an exploded view of that much of the scale assembly seen in FIGS. 4 and 5.

Although the invention is herein particularly concerned with the novel construction of bell-crank levers 21 for weight transfer from the platform 19 to the two side lever assemblies 17 and 18, movable horizontally in closely spaced parallel relationship to the base 20 and thence through motion multiplication levers 24 and 25 to an elongated horizontal plate 37 to stretch the weighing spring 38 and simultaneously operate the rack '52 to turn the pinion for rotating the dial 49 with respect to the usual index wire in the usual window opening in the platform, a brief description will be given of the scale so that the special construction of the novel twopiece sheet metal bell-crank levers 21 can be better appreciated, before these are described in detail by reference to FIGS. 4, 5, and 6.

The scale 16 shown is sustantially rectangular in form and, as previously stated, has a novel complete rearrangement, redesign and reconstruction of the entire lever and weighing mechanism with a view to enabling production of a low scale at least as much as three-quarters of an inch to seven-eighths of an inch lower than what were previously considered low scales. This mechanism includes the two side lever assemblies, 17 and 18 disposed in spaced substantially parallel relation and designed to have a very small vertical movement in a weighing operation in order to permit its being housed between the platform 19 and its base 20 disposed in the unusually closely spaced relationship shown in FIGS. 2 and 3, Where the parts appear substantially full size, the virtual minimum amount of vertical movement given the novel bell-crank levers 21 in the weighing operation causing nearly the same small amount of horizontal movement of intermediate bars 22 reciprocable horizontally in closely spaced relation to the base 20, and that small movement resulting in horizontal oscillation of levers that stretch the weighing spring and operate the weight indicating or readout means through a greater movement. Thus, the outer ends 23 of two inwardly extending mot ion-multiplication levers 24 and 25 are operable by bars 22 to give the required increased amount of movement to the Weight readout mechanism indicated generally by the reference numeral 26 located at the center of the base. The two motion-multiplication levers 24 and 25 are fulcrumed near their outer ends 23 on horizontally disposed hangers 27 that are hooked, as indicated at 28, onto supporting brackets 29 each of which is suitably anchored to the base 20 as by means of a hook on one end entered in a slot in the base and a vertical lug on the other end that is entered in a hole in the base and has its projecting lower end upset to fasten the bracket 29 permanently in place. The inner end of the motionmultiplication lever 25 is notched, as shown at 35, to hook into one end of an elongated yoke 36 mounted in one end of an elongated horizontal plate 37 that has its other end attached to one end of the weighing spring 38 disposed horizontally inside the base 20 with its other end adjustably fixed to a washer 39 that in turn is fixed to one end of a screw 40 threaded in a manually adjustable nut 41 rotatable in a hole provided in the side wall of the base 20. This nut 41 is conveniently arranged with respect to the downwardly projecting flange on the platform 19, to permit easy turning of the nut relative to the screw in making the usual return to zero adjustment of the scale. Yokes 42 of somewhat similar design but much shorter than the yoke 36 are mounted vertically on and near one end of the bars 22, and these have knife edges 43 provided in both ends for fulcrum engagement with the V-notches 44 provided in the outer ends of the motion-multiplication levers 24 and 25. Of course, only one knife edge 43 is employed for each of these two levers in the yokes 42 but, inasmuch as these yokes have reduced lugs 45 which fit in holes 46 provided therefor in the bars 22, as indicated in FIG. 6, the projecting lower ends of the lugs being upset after entry in the holes, the same part 42 can be used with either knife edge 43 engaging in the V-notch 44 in the lever 24 or 25 and there is no need for concern on the assembly line as to which end of the yoke is going to be used for the fulcrum knife edge 43, and, consequently, there is eliminated any likelihood whatsoever of a misassembly. The inner end 47 of the other lever 24 overlaps the inner end 34 of the first mentioned lever 25 inside the yoke 36, as seen in FIG. 1, and has a fulcrum projection 48 pivotally engaging the edge of the lever 25, so that the two levers 24 and 25 both transmit thrust to the elongated plate 37 to stretch the weighing spring 38 and accordingly operate the weight readout mechanism 26 to give the proper weight reading. The weight reading is shown on a horizontally disposed dial 49 visible through the usual window provided in the front end of the platform 19 and readable by the person standing on said platform by reference to the usual index wire mounted on the underside of the platform 19 and bisecting the window opening. The usual lens is provided for magnification of the figures on the dial to facilitate reading, in the window opening. The dial 49 is operable by means of a rack 52 movable positively in one direction with plate 37 and slidably guided for horizontal reciprocation relative to plate 37 by engagement of a T- shaped lug on one "end in a longitudinal slot 53 provided in the plate 37, the rack being urged toward the front end of the slot and laterally against pinion 54 by means of a light tension spring 55 attached to the front end of the rack at one end and to the plate 37 at the other end. This lost-motion at 53 eliminates danger of damage being done to the pinion 54'and rack'52 if a person jumps on the platform. The pinion 54 issuitably mounted for rotation on a vertical axis in a frame 56 that is secured to the base 20 and serves as'a guide for the plate 37 in its reciprocation in each weighing operation. Another light tension spring 57 is stretched on an inclined line between the rear end of the plate 37 and the back wall of the base 20 andserves to support the rear end of said plate' off the base during 'a weighing operation, so that there will be no frictional drag imposed on the operation of the weight indicating means that could result in errors in the readings. The usual tension springs for holding the platform 19 in assembled relation to the base 20 are not shown but are provided at opposite sides of the scale on vertical lines between the base and platform, the places for hooking the lower ends of such springs to the base 20 under tension being indicated at 58.

Referring next to FIGS. 4 and 6, in which the improved form of bell crank levers 21 are shown, it will first of all be noticed that trunnions 64 provided on each of the bellcrank levers 21 are flat on the bottom, as indicated at 65, instead of the usual knife-edge shape like those shown at 66 and 67, for example, on the hangers 68 that are provided under the four corners of the platform 19 to transmit the load of the loaded platform onto the four bellcrank levers 21 through the intermediary of the generally triangular vertical brackets 69 rigid with the generally T- shaped main body portion 70 and on its vertical center line so that the bell-crank lever 21 fulcrumming at on the bracket 59 will under load applied on the platform oscillate through a small angle and transfer the load in a horizontal direction to the horizontal bar 22 inasmuch as the cross-bar 71'on the lower end of the T-shaped body parts extends thorugh a slot 72 in the bar 22 and has fulcrum engagement at its V-shaped portion 73 on the leg of T-shaped part 70 on the knife edge 74 provided in one end of the slot 72. It is due to the fact that, with this novel construction, when load is applied to the bell-crank lever 21 the trunnions 64 are forced to one side of the generally V-shaped notch 75 provided in the bracket 59 that the inclined flat bottoms 76 are required in the lower ends of these notches 75, so that the square side edges on the flat bottoms 65 of trunnions 64 may fulcrum in the wide angle V 77 defined at the junction between one side of each of these notches and the inclined flat bearing surface 76 provided at the bottom of the notch. The interengaging parts are, of course, hardened, and, with this novel form of fulcrum indicated at 65-67 in FIG. 4, much longer life of the scale structure is definitely assured. Ordinaryknife edges would not be adapted for assuming the lateral thrust, and this accordingly necessitated redesign and reconstruction of the fulcrums in order to insure longer life and continued accuracy of weighing. In passing, it will be seen that the middle knife edge 66 on each of the hangers 68 fulcrums in the V-shaped notch 78 provided in the outer end of the bracket 69, while the two other upwardly facing knife edges 67 find similar fulcrum support in the V-shaped notches 79 provided in the lower ends of the two arms of the inverted U-shaped bracket 80 carried on the under side of the platform 19. The

hangers 68, are slightly wider across the top than the inv'erted U-shaped brackets 80 where the lugs 81- on opposite ends project through keystone-shaped h'oles82 provided in the two arms of the U near upper ends; and the hanger 68 is cut away, as indicated at 83, on one sideto provide sufiicient clearance to enter one of the projections 81 in one of the holes 82, after Which it is a simple matter, .by

springing apart the legs of the inverted U-shaped bracket 80, to get the other end 81 entered in the other hole 82. Then the weight of the platform is, of course, transmitted through the notched lower end 79 of the two legs of the bracket 80 through the hanger 68 to the bell-crank 21 and then to the bar 22, the projections 81 serving only to keep the hangers 68 in assembled relationship to the platform 19 by means of the bracket 80.

The novel two-piece construction of the bell-crank levers 21 and 21' is best shown in FIGS. 4, 5, and 6, the latter figure showing the two parts 69 and 70 thereof in exploded relationship to best shown the hook projection 84 on the inner upper end of bracket plate 69 arranged to engage downwardly fairly closely in a notch 85 provided in the top of the T-shaped lever 70 on the vertical center line, for what is eventually one-half of the eventual rigid connection between said parts being provided partly by a substantially square lug 86 provided in right angle relationship to and between the ends of the upper half of the generally V-shaped rear edge 87 of the bracket plate 69 that matches the abutting side of the zigzag or V-bent middle portion 88 of the leg of the T-shaped lever 70, so that this lug 86 is upwardly inclined on a line in converging relationship to the substantially horizontal line of the aforementioned hook projection 84 to insure maximum rigidity when the lug 86 is entered in a novel manner in a square hole 89 that is provided in the part 70 horizontally aligned with the lug, as indicated by dotted line a-b in FIG. 6. The novel method of assembly is as follows: When the two stamped sheet metal parts 69 and 79 are to be assembled together, they are placed in between two specially made dies, whereby the more or less open hook 84 is started in notch 85 at the same time that lug 86 is started in hole 89, and, as the crimp 90 is made in lever 70 transversely of the upper end, between the hole 89 and the trunnions 64 and on a line parallel to the latter, the open hook 84 is entered fully in notch 85 at the same time as lug 86 is entered all the way in hole 89, and then, at the end of this novel assembling operation and before the assembly is removed from between the dies, the protruding end of the lug 86 is upset, as seen at 91, in FIG. 4, and the hook 84, which would otherwise still be a bit open and thereforetend to be loose, is swadged to closed or clinched condition tightly against the outer side of the lower 70, as seen at 92 in FIG. 4. The completed bellcrank assembly is later heat-treated to give the desired hardness on the trunnions 64 and fulcrum bearing surfaces 73 and 78.

It is believed the foregoing description conveys a good understanding of the objects and advantages of our invention.

We claim:

1. As an article of manufacture, a two-piece sheet metal bell-crank lever comprising a generally triangular shaped sheet metal bracket carried on a generally T- shaped sheet metal body member in right angle relationship thereto and on its vertical center line, said T-shaped body member defining aligned trunnions on the ends of the crossbar portion of the T and a fulcrum at the lower end of the leg of the T, there being a downwardly facing hook projection on the bracket at its upper inner end engaging in a notch provided in the T-shaped body at the middle of the top thereof, and a lug projecting from the inner end of said bracket in downwardly spaced relation to said hook which enters and is fastened in a hole provided therefor in said T-shaped body on the vertical center line in downwardly spaced relation to said notch.

2. An article of manufacture as set forth in claim 1 wherein the inner edge of said bracket is in the form of a generally V-shaped projection and matches a generally V-shaped bend in the leg of the T-shaped body, the lug to enter the hole being on the upper half of the V-shaped projection and accordingly on a line generally in converging relation to the line of the hook projection, said T- shaped body having a crimp bent transversely thereof substantially parallel to and below the cross-bar in which the notch receives the hook, whereby the notched crossbar is disposed in a substantially vertical plane but the leg portion having the lug receiving hole therein is inclined relative to said vertical plane and in a plane substantially at right angles to said lug received in said hole.

3. An article of manufacture as set forth in claim 2 wherein the lug protrudes through said hole and its outer end is spread to clinch the connection.

4. An article of manufacture as set forth in claim 2 wherein the hook is flattened against the outer side of the T-shaped body to clinch the connection.

5. An article of manufacture as set forth in claim 1 wherein the trunnions on the T-shaped body member have flat bottom edges in coplanar relationship.

6. An article of manufacture as set forth in claim 1 wherein the upper edge of the bracket has a V-shaped notch provided therein intermediate the ends thereof.

7. An article of manufacture as set forth in claim 1 wherein the leg of said T-shaped body member is bent transversely intermediate the ends to define a fulcrum.

8. An article of manufacture as set forth in claim 1 wherein the leg of said T-shaped body member is bent transversely near the lower end to define a fulcrum, the lower extremity having a cross bar thereon.

FOREIGN PATENTS 4/ 1968 Great Britain.

FRED C. MATTERN, JR., Primary Examiner F. D. SHOEMAKER, Assistant Examiner US. Cl. X.R. 177257 

